The Soviet Union, officially the Union of Soviet Socialist Republics, was a federal socialist state in Northern Eurasia that existed from 1922 to 1991. Nominally a union of multiple national Soviet republics, it was a one-party state prior to 1990 governed by the Communist Party, with Moscow as its capital in its largest republic, the Russian SFSR. Other major urban centers were Leningrad, Kiev, Minsk, Tashkent, Alma-Ata and Novosibirsk. It was the largest country in the world by surface area, spanning over 10,000 kilometers east to west across 11 time zones and over 7,200 kilometers north to south. Its territory included much of Eastern Europe, parts of Northern Europe and Western Asia, and all of Central and North Asia. Its five biomes were tundra, taiga, steppes, desert, and mountains. Its diverse population was officially known as the Soviet people.
The Soviet Union had its roots in the October Revolution of 1917 when the Bolsheviks, headed by Vladimir Lenin, overthrew the Provisional Government that had earlier replaced the monarchy of the Russian Empire.